Guardian Corps.
Kai
The Hero of the game, a robot bearing the crest of the Gravity Circuit who sets out to stop the rampaging Rebel Circuits.
- Amnesiac Hero: Due to Nega shutting down before he could copy his memories, Kai has no memory of the Virus Army's first invasion, and doesn't remember his relationships with the other Circuits well aside from their names.
- Good Is Not Soft: He tries to defuse situations and talk the Rebel Circuits out of what they're doing, but when he fails to do so, will fight them to the death without hesitation if it means protecting others. He also bluntly states Commander Circuit is Beyond Redemption before their battle.
- Grappling-Hook Pistol: Kai's hookshot ability allows him to shoot out an energy projectile that lets him swing off of ceilings and attack enemies from far away.
- Rapid-Fire Fisticuffs: His primary means of attacking is through punching, and he can land punches pretty fast. This works good enough for common enemies, but not so much for bosses, who become invincible for a moment after being damaged a lot in a short time.
- Red Is Heroic: He's associated with a vibrant red - his armor paint is even called "Heroic Red".
- Resurrective Immortality: Thanks to the Gravity Circuit, if Kai gets destroyed, he simply copies his core programming to a repair station and gets back in the fight.
- This Is Unforgivable!: After having to kill Kernel in self-defense, he declares that he'll never forgive Commander Circuit for hijacking Kernel.
- Wrestler in All of Us: One of the Burst Techniques he can unlock from the start is the Heavenly Piledrive, a piledriver that deals a load of damage to enemies.
Kernel
The current leader of the Guardian Corps., an eccentric military bot who directs Kai on how to fight the Virus Army.
- Benevolent Boss: He's pretty kind to Kai and the rest of the Guardian Corps., being quick to praise them for their efforts.
- Brainwashed and Crazy: He gets hijacked by the Commander Circuit over the course of the game, with him being fully corrupted once all eight Circuits have been defeated.
- Crouching Moron, Hidden Badass: He's a bit pompous and frequently has his priorities mixed up, but he earned his position through his evacuation efforts during the first Virus Army invasion and can go mostly toe-to-toe with Kai.
- Skewed Priorities: A Running Gag has him cap off his briefings with asking something of Kai that's very tangential towards stopping the Rebel Circuits.
Pat
One of the Guardian Corps.'s troopers, he idolizes the Gravity Circuit and maintains a list of challenges that he'd like to see his hero complete.
- Fanboy: He very strongly idolizes Kai, referring to him as "Master Kai" as an honorific.
- Lovable Coward: He's described as being a bit of a coward, but is pretty well-trusted by the Guardian Corps. despite it, and nobody questions him taking Kernel's position as the Guardian Corps. commander when Kernel gets hijacked.
- You Are in Command Now: When Commander Circuit finishes hijacking Kernel, Pat takes over Kernel's role for sending Kai out on missions.
Nega (UNMARKED SPOILERS)
A humble trader bot specializing in sharing stories and Burst Techniques, who seems to know quite a lot about the Circuits.
In actuality, he's the previous Gravity Circuit who fought the Virus Army all those years ago and was left in a powered-down state, leaving his Circuit to take another bot as its wielder.
- Heroic Sacrifice: After Kai defeats the Commander Circuit, he claims the Circuit for his own to ensure the common bots will continue to function, knowing he'll be unable to leave the Ark if he does and seeing it as a fitting way to atone for his part in the Virus Army mess.
- In the Hood: He remains hooded until he's encountered in the first Ark stage, so as to keep his status as the former Gravity Circuit hidden. His cloak is actually one of the window curtains from the Guardian Corps. HQ.
- Legacy Character: He mentions that he's probably not the first Gravity Circuit, but he was the one who came before Kai.
- Made of Iron: He takes three entire health bars' worth of a beating from Kai during his boss battle, and not only manages to survive but is still able to help him open the pathway to the core of the Ark.
- Mirror Boss: He uses Kai's moveset during his boss battle, equips power-up chips during his second phase, and can use the four basic Burst Techniques.
- One-Steve Limit: The reason he calls himself Nega is to avoid confusion with Kai.
- Red Oni, Blue Oni: Amusingly, he's the red to Kai's blue, being a little more playful than Kai's normally composed self and even joking about making a Heroic Sacrifice for the good of the world's inhabitants.
Virus Army and Rebel Circuits
Ray
- Blood Knight: He's the quickest of the Circuits to jump towards facing Kai in combat.
- Clock King: A few lines about him indicate that he's rather obsessed with punctuality and making sure everything runs on schedule, to the point where he admonishes Kai for how long it took him to reach Ray's boss room.
- Kill It with Fire: In addition to his burning-hot lasers, Ray has a flamethrower stored in his arms and can shoot fireballs from his shoulders.
- Slow Laser: His specialty as the Optic Circuit is hot lasers that travel slower than light, but pack a serious punch and can reflect off of panels to make dodging trickier.
- Wave-Motion Gun: His Burst Technique, Burning Laser, has him fire several screen-filling lasers in quick succession.
Trace
- Face Death with Dignity: When defeated, she laments that her experiments didn't work out and wishes Kai good luck in defeating the other Rebel Circuits.
- Labcoat of Science and Medicine: She's wearing one that doubles as a Badass Cape.
- The Medic: Before becoming a Rebel Circuit, Trace specialized in patching up common bots and the other Circuits.
- Necromancer: In the modern day, she's effectively a robot necromancer, and the second half of her Burst Technique has her create some zombie minions.
Blade
- Blow You Away: In addition to his ice attacks, he has a giant fan on his back that he uses for flight and weaponizes during his Burst Technique.
- An Ice Person: As the Cooler Circuit, he has the ability to painfully freeze machines solid and uses ice-based projectiles.
- Pungeon Master: He makes a few cold-related puns before his battle.
Cable
- Shock and Awe: His specialty as the Power Circuit is controlling electricity, with his attacks and Burst Technique being electricity-themed.
Bit
- Blood Knight: He's very eager for Kai to show him his moves once the two come face to face, bluntly refusing to give up without a fight.
- Graceful Loser: When Kai defeats him, he calmly compliments Kai and tells him not to feel bad for him just before he explodes.
- The Only One Allowed to Defeat You: He destroys a Virus Army helicopter so that he can confront Kai.
Medley
The bearer of the Wave Circuit, Medley specializes in communications and sound waves. As a Rebel Circuit, she's decided to throw a massive concert in the City Center, bringing the Virus Army with her.
- Dance Battler: Her combat style involves a lot of stylish pirouettes and dance moves.
- Gale-Force Sound: She creates shockwaves of sound when she lands, and her Burst Technique has her summon speakers that deal damage in a radius around them.
Crash
- Gentle Giant: He's the most level-headed of the Rebel Circuits, regretting that he and Kai have to fight and trying to give him a vague warning about the Virus Army's origins.
- This Is a Drill: He carries a huge drill on him that he can shoot out like Kai's hookshot.
Hash
- The Cracker: He specializes in hacking and the setup for his stage is to stop him from hacking important infrastructure.
- I Shall Taunt You: He'll occasionally laugh at Kai, leaving him open for punishment.
- Multi-Armed and Dangerous: He's got four arms, unlike the rest of the Circuits.
The Mastermind (UNMARKED SPOILERS)
The Commander Circuit is the tenth Circuit of the Ark, and the originator of the Virus Army.
Embittered by the other Circuits betraying their original mission, and cast down to the depths of the Ark, the Commander schemes to bring them all back so he can finally return to the stars.
- Barrier Warrior: One of his signature Burst Techniques is Burst Shield, which he uses to protect the hijacked Kernel during his second phase and which he himself uses to shield himself.
- Damage-Sponge Boss: Not only does he have three health bars, he also takes reduced damage from the hookshot and shields his weak point starting from the second phase.
- Evil Cannot Comprehend Good: He can't comprehend why the Circuits defected to save the common bots, thinking they wanted to be worshipped by the bots and stating that if they wanted that, they could have asked him to make them worship the Circuits.
- Final Boss: Destroying him is the last challenge of the game's story.
- Just a Machine: A rare case where it's a machine holding this viewpoint about other machines - the Commander Circuit regards the common bots the other Circuits wanted to protect as disposable trash.
- Knight of Cerebus: When he starts making his presence known, the mood of the game rapidly darkens, and doesn't come back until he's defeated.
- Tactical Suicide Boss: On his final phase, he uses his second Burst Technique, Virus Command, to summon enemies to help fight Kai for him. This can backfire on him, as Kai can grab the enemies and throw them back at him to instantly break his shield or do damage to him.
